(Reuters) - Burger King Worldwide Inc, known for its "Whopper" hamburgers, has introduced lower-fat french fries as consumer groups and nutrition experts in the United States increase pressure on the food industry to offer healthier alternatives.

The Miami-based hamburger chain late on Monday said its new "Satisfries" contain 40 percent less fat and 30 percent fewer calories than those sold by archrival McDonald's Corp, which is widely considered to have the fast-food industry's most popular french fries.

McDonald's declined on Tuesday to say whether it will offer its own lower-fat fries.

Some restaurant operators are embracing healthier food in large part because many consumers will pay a bit more for it.

To that end, Burger King will sell its new fries for a premium, at a suggested price of $1.89 for a small portion versus $1.59 for its existing fries. A small serving of the new Satisfries has 270 calories and 11 grams of fat, while the older Burger King fries have 340 calories and 15 grams of fat.

Burger King's new fries are crinkle-cut and thinly coated with a batter that absorbs less oil, the company said. They were developed in partnership with french fry supplier McCain Foods and are exclusive to Burger King, a spokeswoman told Reuters.

More than one-third of Americans are obese, and about 10 percent of the U.S. healthcare bill is tied to obesity-related illnesses such as Type 2 diabetes, heart disease and hypertension, according to the Organization for Economic Co-operation and Development.

The Center for Science in the Public Interest is among the groups lobbying the U.S. food industry to make healthier products.

Margo Wootan, its director of nutrition policy, called Burger King's new fries a "step in the right direction" and urged the chain to do more.

"If people are going to eat fries, the new fries are an improvement," Wootan said. "Now Burger King needs to get as inventive with other vegetables and add more to the menu."